The present invention relates to a device for coating bulk material. A device for coating bulk material is described in East German Patent No. 25 75 54, which describes a device that includes a rotating holder for accommodating bulk material to be coated, as well as a plasmatron sputter source arranged within the rotating holder. The plasmatron sputter source is directed downward, such that the bulk material to be coated always stays within its sphere of action during the rotation of the rotating holder. Located on the inner wall of the rotating holder are control devices which ensure good intermixture of the bulk material during the rotation. The device allows the manufacture of single-layer metallic coatings having average adherence. The device does not possess means for producing layers having specific predefined properties. Thus, in particular process steps for increasing the adherence of an applied coating, or the production of multilayer systems, are not shown.
Another vacuum bulk-material coating device, in which the bulk material to be coated is moved in a rotating holder about a coating source, is described by the German Patent No. 42 09 384. Used here as the coating source is an electron-bean vaporizer which--subject to the principle--acts upwards. To produce high-quality coatings, also located in the interior of the rotating holder is a plasma or ion source whose direction of action is rotated by approximately 120 degrees with respect to the electron-beam vaporizer. For the coating process, the rotating holder is set into fast rotation. The centrifugal force occurring in so doing holds the bulk material to be coated against the inner wall of the rotating holder. The bulk material thus fixed against the inner wall of the rotating holder is conveyed in succession through the spheres of action of the electron-beam vaporizer and of the plasma/ion source. A stripping-off device engaging in the upper area of the rotating holder loosens the bulk material from the inner wall, and thereby constantly changes the position of the bulk material to be coated. This device permits coatings to be produced having different properties according to the present invention. However, the necessary rapid rotation of the rotating holder, in conjunction with the stripping process engaging in a correspondingly hard manner, leads easily to damage of the components to be coated. Therefore, particularly in the case of components having many edges, one must be prepared for a high rate of reject material.
To bring about specific physical properties for a coating, it is furthermore known (from German Published Patent Application Nos. 42 39 843 and 43 43 354) to carry out the coating process, while adding reactive gases in variable concentrations. However, known coating devices of this type are restricted to the coating of stationary objects, and do not allow coating of bulk goods.